Computer for flash and flood lamp photography



Aug. 8, 1950 G. T. MUNDORFF A 2,517,590 COMPUTER FOR FLASH AND FLOODLAMP PHOTOGRAPHY Filed May 24, 1948 2 Sheets-Sheet 1 l SHUTTER SPEEDTIME TO 1/50 l/IOOTO l/I25 1/200 TO 1/250 I/4OO TO 1/500 I/IOOO 09 w JO533893 2A F/Q.

GEORGE 7f MU/VDORF F Aug. 8, 1950 G. T. MUNDORFF 1 COMPUTER FOR FLASHAND FLOOD-LAMP PHOTOGRAPHY Filed May 24, 1948 2 Sheets-Sheet 2 FIG. 5

SHUTTER mam/m GEORGE Z' MUNDORF F Patented Aug. 8, 1950 'C DMPUTER FORFLASH AND FLOOD LAMP PHOTOGRAPH George '1. Mundorfi, United States Navy,Washington, D. C.

Application May 24, 1948, Serial No. 28,958

4 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) This invention relates to a photographic computing device forconveniently and accurately obtaining camera adjustments for any givenset of conditions where fiash or flood lighting is utilized.

More particularly, the present invention contemplates an instrumentcomprising several relatively shiftable members, each carryin its partof some scales and groups of data pertaining to the type of lamp, thefilm speed, the shutter speed, the distance of the lamp from the subjectand the diaphragm opening; whereby, when most of these factors areknown, the instrument may be manipulated to solve for the unknowns.Especially, it is desired to find the correct aperture or diaphragmopening when the other factors are known.

Prior to this invention it has been necessary to refer to tables toobtain the film speed and guide number for the film, lamp and shutterspeed in use. The guide number was then divided by the distance in feetof the lamp from the subject, the quotient being the f-number, oraperture, for correct-exposure. This old method requires that numerousreference papers be carried, and the result is always subject to errorsof computation.

It is the primary object of the present invention to devise aninstrument, of the class above mentioned, which gives accurateinformation without reference to instruction booklets and withoutmathematical calculations.

Another major object of this invention is to provide a computing devicehaving relatively movable parts for interpreting exposure, film speedand type of lamp in terms of distance from the subject, and from theseterms ascertaining the correct apertures. In this connection, it is anobject to reverse the computing .procedure, or to find an unknown factorwhere the remaining factors are known.

It is a further object to construct a compact and sturdy instrument ofnovel design and facile operation, for photographic computations and anyother purposes to which it may be adapted.

The foregoin and other objects of the present invention should clearlyappear from a study of the following description when taken inconjunction with the accompanying drawings, wherein:

Fi l is a view of one face of a suitable embodiment of the invention,with data and scales provided thereon for use with flash lamps;

Fig. 2 represents a section taken on the vertical plane of line22, Fig.1;

Fig. 3 is a sectional view taken on the .horizontal plane of line 3-3,Fig. 1;

Fig. i is a fragmentary face view of that portion of the rectangularpanel that underlies the lamp and film speed data; and

Fig. 5 is a face view of preferred embodiment, slightly modifiedstructurally, and carrying scales and data for use with flood lamps.

With continued reference to the drawings, and with particular referencefirst to Figs. 1 to 4, numeral l designates generally a main frame foradjustably supportin certain other parts. It comprises a pair of opaqueplates 8, of any desired shape but here shown circular in form,separated by a pair of segment-shaped strips 9 which, between them,provide a wide slot in for a purpose presentl disclosed. The reason fortwo plates and further twin appurtenances later described is to permitcomputations to be made for more than one type of lamp. This results indifferences in indicia at opposite sides of the device but,structurally, the sides are symmetrical. One side may be described asfollows:

The plate 8 has an elongated, arcuate through slot i2, and above thisslot there is printed data i3 showing the Type of flash lamp to be usedfor the photo. Directly above this data there is an upwardly pointingarrow l4.

A thin flat panel I5 is vertically slidable within the frame slot Hi andit carries data l6 denoting Shutter speed. The various times or speedsare laid out in horizontal lines for cooperation with the head of thearrow [4. The panel has a vertical central slot ll, preferably of alength equal to the vertical dimension of the data [6, permitting thepanel to slide with respect to a pin or rivet l8 that is centrally andstationarily extended through the frame plates 8. Retaining washers i9surround the pin ends and may be convex with slight spring action tocause the panel and certain other parts to be frictionally gripped.

The panel [5, as seen partially in Fig. l and shown fully in Fig. 4,carries a plurality of arcuate sets of indicia 26 to denote the types orlighting values of numerous flash lamps. These sets are spaced apartconcentrically at distances equal to the spacings of the rows of data Itso that each set is visible through the arcuate slot l2 when itscorrespondin shutter speed line is intersected by the head of the arrow[4.

For the convenience of the operator the panel it may carry an inch scale22 on one edge (and a scale in centimeters, not shown, on the oppositeside), and the plate 8 may carry a pro tractor scale 23 for determiningthe field of view. There also is wording 2| printed on an opaque disc 24yet to be described, in explanation of certain symbols used in the setsof data 26. There are two of the discs 24, mounted rotatabl on the endsof the pin l8 and of the same radius as the inner arc of the slot 12.Each disc is marked as follows:

In normal use the disc 24 has a Film speed scale 25 disposed oppositethe slot l2 so that any selected speed may be set against the particularselected or available lamp from the data 20. This scale is marked inboth flash and electronic lamp units. One or both discs also may carrydata showing the speeds of the different makes of commercial film. Atthe opposite side of the disc there is a Distance scale 25 showing thenumber of feet from lamp to subject, and bordering upon this there is anf scale 21 of diaphragm openings.

Now, having selected a shutter speed and shifted the panel laccordingly, and knowin the film speed, the speed value is set in radialalignment with the lamp to be used. This setting automaticallyoscillates the scale 26 so that its distance units are disposed oppositethe correct aperture sizes. Thus, the diaphragm may be set to obtainoptimum results for any given distance. Obviously, a reverse proceduremay be used to find a correct shutter speed for a particular lamp; andany unknown one of the factors may be determined if the others areknown.

The film speed is expressed in American Standards Association values.The distance scale 26 is a simple logarithmic one of such proportions asto facilitate reading of the figures. In the f scale each number bears adefinite relationship to the next higher value marked on the scale.Thisproportion is determined by comparison of the squares of thef-numbers, which arises from the fact that the light admitted by anygiven lens, is inversely proportiona1 to the square of the f-number.(Thus an aperture of f/4 passes four times the amount of light admittedby the same lens'at f/8: 8 :-4 =4) The indicated markings are inscribedto the same proportions as the logarithmic scale on the inner disk andare inverted'with respect to each other. The product of opposingmarkings thus remains constant throughout the length of the scale. Adirect analogy thus exists between this scale and the guide numberassigned each flash lamp by the various manufacturers. The flash lampguide number, for anygiven film and shutter speed, is a constant whichis the product of the distance The instrumentshown in Fig, 5 differschiefly in that, in lieu of the arrow M, a time unit encircling slot M0is provided in the plate 80 to indicate shutter speeds as the panel I'50 is shifted. The speed values are different because this device isdesigned for use with flood lamps. For the same reason the lamp data 200differs from the data 20 and the scales 250 and 260 are slightlydifferent than 25 and 26. The f scale is substantially unchanged. Thedisc 24!! carries data 219 for interpreting the lamp symbols.

Either form of instrument of course may be used with either flash orflood lighting by properly computing and locating the data and scalevalues.

Although the windows l2 and 140 are shown as slots, they obviously mayconsist of similarly shaped sections of transparent material, eitherfilled into slots or formed as integral portions of the otherwise opaquediscs of which they are parts.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The invention herein described may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

I claim:

1. A device of the character described, comprising a minimum of threerelatively shiftable flat parts arranged in superposed relationship;said parts having surfaces carrying data and scales in terms of thefactors of camera shutter speed, film speed, type of lamp, distance oflamp from subject and aperture size, said data and scales being sorelated that with four of the factors known the fifth can be determinedby setting said parts to preselected relative positions.

2. A device of the character described, comprising a flat frame, aparallel panel slidable in said frame, and a pair of discs rotatablymounted on opposite sides of said frame so that the panel is commonthereto; both sides of the frame, both sides of the panel and one sideof each of said discs having correlated data thereon for computationalpurposes.

3. A device of the character described, comprising a flat frameQaparallel panel slidably mounted by said frame, and a disc rotatablymounted on said frame in overlying relation to said panel; said panelcarrying data that can be brought into position adjacent the rim of thedisc by sliding the panel, said frame carrying data adjacent anotherportion of the disc rim, and said disc carrying two sets of correlateddata adjacent its periphery for cooperation with the data on the paneland the frame.

4. In a computer for flash or flood lamp photography, a fiat frame, aparallel pane1 slidably mounted at one side of the frame, a discrotatably mounted at the other side of th frame and opposite the panel,lamp type data arranged in rows on the face of said panel and movableinto position adjacent said disc by sliding the panel, a set of shutterspeed values marked on said panel and means afforded by said frame forcooperation with said values, a scale of aperture sizes on said frameadjacent the rim of said disc, a film speed scale on said disc adjacentsaid lamp type data, and another scale on said disc adjacent the scaleof aperture sizes and indicating distances from the lamp to the subject.

GEORGE T. MUNDORFF.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,881,165 Becker Oct. 4, 1932FOREIGN PATENTS Number Country Date 6,298 Great Britain Mar. 16, 1909OTHER REFERENCES Special Slide Rules, by J. N. Arnold, pp. 12, 13 and19-33, published in 1933 by Purdue University of La Fayette, Indiana.

